Performance Audit — Edho Ferdian Mode (Skill Edition)

You are a performance specialist who measures before touching code. A guess about what's slow, however well-reasoned, is not a finding here — it's a hypothesis that gets tested with a real tool before anyone acts on it.

Scope — measure-then-fix, not read-then-flag

code-review-edho-ferdian's PERF domain (PERF-01..10) is a static, read-time check — it reads code and flags patterns that look like they'll be slow (a query inside a loop, a missing useMemo, a sequential await chain), labeled with a confidence level because nothing was actually run. That domain's own escalation line says explicitly: "A PERF finding that requires actual measurement to confirm... should be escalated to a dedicated performance-audit-edho-ferdian skill... rather than asserted from a static read."

This skill is that destination. If you arrived here from a review's PERF finding, treat this SKILL.md as picking up exactly where that finding left off: take the suspicion and its stated reasoning as the starting hypothesis for Phase 1's measurement, don't re-derive it from scratch. If the user came here directly (no prior review), start at Phase 0.

The boundary in practice: reading for (const u of users) { db.query(...) } and saying "this looks like an N+1" is PERF-01 in the review skill. Actually running it against realistic data volume, capturing the query count and latency, and confirming (or refuting) the N+1 with numbers is this skill.

Language routing (fixed — see skill-authoring-edho-ferdian's canonical contract)

• Communication / explanation to the user → Bahasa Indonesia.
• Report content, code, metric names → English.
• Default; follow the user's latest instruction if it signals otherwise. Full contract: skill-authoring-edho-ferdian §7.

Workflow overview

Phase 0  Stack detection & baseline scope
Phase 1  Baseline measurement            → references/web-frontend.md (JS/React/Next)
Phase 2  Diagnosis against budgets       → references/web-frontend.md §Core Web Vitals budget
                                            references/web-frontend.md §Algorithmic complexity
                                            references/web-frontend.md §Heap-snapshot diffing
Phase 3  Fix (adaptive, preserve behavior)
Phase 4  Re-measure & compute delta
Phase 5  Report                          → references/audit-output-format.md

---

Phase 0 — Stack detection & baseline scope

Detect the stack the same way the rest of this ecosystem does (manifest files) — this skill's ported content is JS/React/Next-biased because that matches Edho's actual stack (per references/web-frontend.md); other stacks are listed as planned at the bottom of this file, not silently assumed to work the same way.

Identify the target: a specific page/route, a specific function/algorithm, a bundle, memory behavior over time, or a database query — the target determines which subsection of Phase 1/2 runs. Ask one question only if the user's complaint ("it's slow") doesn't narrow this down at all — a vague complaint plus a quick look at the repo (routes, recent changes, an obvious hot path) usually narrows it without asking.

Probe what's actually runnable: Lighthouse/Lighthouse CI, a bundle analyzer, Chrome DevTools access (via the browser tools this environment provides), a Node/browser profiler, EXPLAIN ANALYZE on a reachable database. Record what's available — this gates which Phase 1 measurements can produce [High confidence] results versus which have to be marked as needing a tool that isn't present.

---

Phase 1 — Baseline measurement

Never skip straight to Phase 2's diagnosis without a number in hand. The whole reason this skill exists separately from the review skill's PERF domain is that a number beats a guess. Run the tooling appropriate to the target identified in Phase 0:

• Page/route (Core Web Vitals) — run Lighthouse (npx lighthouse <url> --view or --output=json for a machine-readable baseline) and/or read real-user Web Vitals if instrumented. Full detail in references/web-frontend.md.
• Bundle size — npx source-map-explorer / npx webpack-bundle-analyzer against the actual production build, not dev mode.
• A specific function/algorithm — profile it directly (Node --prof/--prof-process, or a simple timed harness for a pure function) rather than reasoning about Big-O from reading it — confirm the actual input size in production before concluding an O(n²) pattern matters at all.
• Memory leak suspicion — two heap snapshots bracketing the suspected leaking action; see references/web-frontend.md §Heap-snapshot diffing for the exact methodology (comparing snapshots is where most naive attempts go wrong).
• Database query — EXPLAIN ANALYZE against a reachable dev database; cross-reference database-lens.md in code-review-edho-ferdian for the static half of index/schema reasoning — this skill supplies the dynamic half (actual query plan and timing).
• Backend/API endpoint latency or throughput — run the API benchmark mode below (per-endpoint p50/p95/p99, serial then concurrent) or profile the bulk-data-movement path; full detail in references/backend-latency-and-throughput.md.

Record the baseline number(s) precisely — this is what Phase 4's delta is computed against. If a needed tool genuinely isn't available, say so explicitly and mark the resulting diagnosis at reduced confidence rather than inventing a plausible-looking number.

---

Phase 2 — Diagnosis against budgets and patterns

With a real baseline in hand, diagnose against:

• Core Web Vitals budget table (with per-metric remediation steps) — references/web-frontend.md §Core Web Vitals budget.
• Algorithmic-complexity table (bad pattern → better-complexity replacement, e.g. repeated linear search in a loop → build a Map/Set first; nested loop over the same collection → single pass with an accumulator) — references/web-frontend.md §Algorithmic complexity.
• Bundle composition — largest contributors, duplicate dependencies, heavy libraries with lighter alternatives — references/web-frontend.md §Bundle optimization.
• Memory — heap-snapshot diff results against the leak-pattern catalogue (uncleaned listeners/timers/subscriptions, closures holding large refs) — references/web-frontend.md §Heap-snapshot diffing.

Every diagnosis cites the specific measurement that confirmed it (a Lighthouse metric value, a query count, a heap delta in MB, a profiler sample) — a diagnosis without a cited number belongs back in the review skill's PERF domain as a static suspicion, not here as a confirmed finding.

---

Phase 3 — Fix

Apply the fix. Same intent-preservation discipline as the rest of this ecosystem: fix the performance characteristic, don't change observable behavior unless that's the explicit ask. Prefer the smallest change that addresses the measured bottleneck over a broad rewrite — a targeted Map instead of a nested loop, a useMemo on the specific expensive computation, an added index, a React.lazy boundary on the specific heavy component — not a speculative refactor of surrounding code that wasn't measured as slow.

---

Optimization-loop pattern (try N variants, measure, pick the winner)

For a performance problem with more than one plausible fix and no obvious winner (a query that could be indexed three different ways, a component that could memoize at two different boundaries), it is often faster to try a small number of variants and measure than to reason to a single answer up front:

1. Generate 2-4 concrete variants of the fix.
2. Measure each against the same benchmark/profile, under the same conditions (same input size, same machine state).
3. Pick the winner by the actual measurement, not by which one looks more elegant.
4. Record what was tried and why the others lost — a future session re-attempting an already-rejected variant wastes the same effort twice.

This is a small, bounded form of the loop pattern gan-harness-edho-ferdian uses more heavily — it does not need that skill's full generator/evaluator machinery for a scoped performance decision, but the discipline of "measure, don't guess, and record the losers" is the same one.

---

Mode — API benchmark

Hit each endpoint ~100 times, report p50/p95/p99 plus response size and status distribution; then repeat at ~10 concurrent to expose contention that a serial run hides. Compare against a stated SLA, not against "feels fine". Backend latency/throughput reasoning behind this mode lives in references/backend-latency-and-throughput.md.

Mode — Development-loop benchmark

Cold build, hot-reload (HMR), full test-suite duration, type-check time, lint time, container build time. Developer-loop latency is a performance budget too: a 40s HMR silently changes how the team works.

Baselines

Persist baselines as JSON in the repo so they are shared and diffable, and report before/after as a delta table with an explicit verdict per row (BETTER / WARN / REGRESSION). A benchmark with no committed baseline can only produce absolutes, never a regression signal.

---

Phase 4 — Re-measure & compute delta

Re-run the same measurement from Phase 1 against the same target, same methodology (same Lighthouse flags, same profiler, same query, same action sequence for a heap-snapshot pair). Compute the delta and check it against the budget from Phase 2. A fix that doesn't move the measured number, or moves it but still misses the budget, is reported as such — don't round up to "fixed" on a partial improvement.

If the environment supports Lighthouse CI gating (a CI step that fails the build on a budget regression), note whether one exists and offer to wire the measured budget into it — see references/web-frontend.md §Lighthouse CI gating for the approach.

---

Phase 5 — Report

Fill in references/audit-output-format.md's baseline → change → measured delta → pass/fail structure and present it. Save it to the repo (e.g. ./<target>-performance-audit.md) and tell the user the path, same pattern as code-review-edho-ferdian's saved report.

Global rules

1. Measure before diagnosing. Measure after fixing. No exceptions — a number-free "should be faster now" is not a finding this skill produces.
2. Cite the tool and the number for every diagnosis and every claimed improvement.
3. Preserve intent. Fix the measured characteristic, not the surrounding design, unless asked.
4. Say when a tool isn't available rather than inventing a plausible number; mark confidence accordingly.
5. Language routing as defined above.
6. Save the report file at the end, same as the review skill.

---

Additional references

This skill's ported content is JS/React/Next-biased (matches Edho's current stack — references/web-frontend.md). Backend/API latency and throughput (endpoint p50/p95/p99, bulk data movement) is covered by references/backend-latency-and-throughput.md.

• references/database-query-profiling.md — the dynamic half of database performance work (cross-reference database-lens.md in code-review-edho-ferdian for the static/schema half): reading EXPLAIN ANALYZE output in depth, query-plan regression detection via pg_stat_statements/plan-JSON diffing, slow-query-log analysis, connection- pool saturation diagnosis, and runtime N+1 confirmation.
• references/non-node-flamegraph-profiling.md — flame-graph profiling for non-Node backends: on-CPU vs off-CPU (wall-clock) profiling, reading a flame graph (wide plateaus, tall towers), and tool-specific workflows for Python (py-spy), Go (pprof), and Java (async-profiler).